The auditory system derives the location of a sound source from multiple acoustic cues. The strategies of information processing used by the auditory system to evaluate and integrate these cues will be studied with extracellular recording techniques in the barn owl. Neuronal activity that reflects auditory spatial analysis is found in the optic tectum, where neurons are sharply tuned for sound source location and are organized according to their spatial tuning to form a physiological map of space. Digitally synthesized sounds delivered dichotically and in a free-field will be used to elucidate the integrative basis of their spatial tuning and of the space map. The underlying processes involve the real-time analysis of time-varying complex signals, the comparison and exact evaluation of differences in signals at the two ears, and the detection of particular sets of cues that are associated with appropriate locations in space. Revealing the mechanisms by which these functions are carried out will broaden substantially our understanding of information processing in the nervous system. Auditory experience during early life shapes sound localization behavior and the spatial tuning of neurons in the optic tectum; pilot studies indicate that early visual experience has a similar influence on these auditory functions. Behavioral experiments will investigate the role of vision in the development of sound localization. The sensitive and critical periods will be elucidated and the neural basis of this developmental plasticity will be sought. Answers to questions such as how and where experience exerts its influence on brain development and what causes the brain to become refractory to this influence after the end of the critical period will provide a foundation for formulating optimal therapeutic procedures for the prevention of perceptual handicaps (such as language impairment and learning disorders) and the recovery of mental function, especially among individuals who have suffered sensory losses early in life.